At present, the capacity for identifying candidate drugs exceeds the capacity for toxicological screening. If large panels of drug candidates could be rapidly and accurately screened in vitro for both activity and predicted toxicity, those with the best in vitro therapeutic index could be advanced for further study, increasing the rate of success for advanced candidates and decreasing the cost of drug development. Trellis Bioscience and Tissuelnformatics, Inc. are proposing to combine their technologies to deliver a practical, high throughput assay for in vitro toxicity. Trellis is expert in the use of nanoscale multihued beads as labels in multiplexed assays of specific biomolecules. Tissuelnformatics has developed microscope systems and computational techniques for histomorphometric analysis of tissues, with applications including examples of toxicant-treated tissue. In effect, Trellis provides high contrast staining for multiple key features, facilitating the multivariate pattern recognition and classification software provided by Tissuelnformatics. Preliminary data show that intracellular structures in frozen liver sections can be labeled with Trellis' antibody-conjugated fluorescent beads, extending prior work at Trellis on cultured cells. Thus, a major proof of concept for this project has already been accomplished. The Specific Aims of this Phase I proposal are: 1. Optimize multihue bead staining protocols for liver tissue slices 2. Develop preprocessing protocols and analytical metrics for the analysis of bead distribution 3. Determine the quantity and distribution of key molecular markers in liver slices after exposure to three common toxicants. In Phase II, the technology will be expanded to include a larger set of markers selected from those proteins known to be suitable biomarkers of toxic responses and correlated to morphological change. Related and unrelated toxicants will be tested to establish the degree of clustering in results as a function of toxicant class. Tissues to be tested will be expanded to include kidney, heart muscle and lymphocytes.